The most likely explination is that something interrupted the write session so a file hadn't finished writing. This causes card errors but you may be able to recover the files (other than the bad one) using a recovery program. Things that might have been the cause are opening the card door, weak battery, turning off during a write session (saving photo files from the buffer to the card) or maybe a bad card
"A skill is developed through constant practice with a passion to improve, not bought."
